Acoustical device



Feb. 22, 1938. A. E. N LAWRANCE 2,109,012

ACOUSTICAL DEVICE Filed Feb. 27, 1956 2 Sheets-Sheet 1 Feb. 22, 1938 A.E. N. LAWRANCE 1 ACOUSTICAL DEVICE Filed Feb. 27, 1936 2 Sheets-Sheet 2'Patented Feb. 22, 1938 ACOUSTICAL DEVICE Athol Ernest Neville Lawrance,Johannesburg,

Transvaal, Union of South Africa Application February 27, 1936, SerialNo. 66,100

8 Claims.

The present invention relates to acoustical devices such as microphones,loud speakers, horns, cabinets, phonographs and musical instruments, andits object is to provide even response and entire non-resonance to soundwaves of the different frequencies employed in speech and music.

According to the invention, an acoustical device comprising a channel ortube having a conical, prismatic, cylindrical or like shape andsuccessive longitudinal elements of the device vary in stiffness andform a continuously progressive series embracing the wholecross-sectional periphery of the device.

Embodiments of the invention are illustrated in the accompanyingdrawings in which:

Figure I shows a speech coil in perspective.

Figure II is a plan view of an unfolded speech coil.

Figure III shows a cross-section of the speech coil of Figure II.

Figure IV shows a modified construction of speech coil.

Figure V shows a cross-section of Figure IV.

Figure VI shows a horn construction in perspective.

Figure VII is an end view of the horn of Figure :VI.

Figure VIII is an end view of a modified construction of horn.

Figure IX is a plan of another horn construction, and

Figure X shows a transverse section of the horn of Figure IX.

Figures XI and XII show other modified forms of speech coil or channel.

Figures XIII to XVI show other modified forms of speech channel.

Referring to Figure I, this shows a speech coil former of cylindricalshape, a portion 2 of which is occupied by a coil of wire 3 to whichconnections aremade by leads 4 and 5. A speech coil wound on acylindrical former in this manner may be employed in a moving coilloudspeaker or a moving coil microphone, as is known. The former onwhich the coil is wound is made of stiff but very light material andcomprises successive longitudinal elements which vary in stiffness andform a continuously progressive series embracing the wholecross-sectional periphery of the former. This variation in stiffness mayrefer to the whole of the former but in\ the arrangement shown in FigureI it applies only to the unwound portion 6. Figure II shows the formerunrolled. The portion 2 is the wound portion and the portion 6 is theunwound portion, the successive elements], 8, 9

and I of which vary in stiffness. The variation in stiffness is effectedby making these portions of different thickness as shown in Figure 111.

The speech coil is preferably constructed by taking a plain cylindricalor other shaped former, of uniform stiffness around the whole of itscross-sectional periphery comprising the whole area 2, 6 and attachingto the portion 6 successive strips of very thin material, such as tissuepaper, by means of glue or other adhesive. The first strip 9, greatestin length viz. of the length of the circumference of the former, is thenapplied in the manner shown in the drawings. A second strip 8, thelength of the circumference of the former is then superimposed and athird strip I, the length of the circumference of the former is thensuperimposed on the other two. The leads 4 and to the coil of wire aresecured to the thickest part I of the former. The use of three separateadditional strips has been shown, but any number suitably varying inlength may be used. Due to their different thicknesses and mass, thedifferent longitudinal elements of the speech coll have differcutstiflnesses and elasticity and therefore respond differently to thevarious speech frequencies employed, the result being that the overallresponse is very even and free from resonance. Owing to the usethroughout of extremely thin material for the portion 2, 6 and for thelaminatlons superimposed thereon, the speech coil former can be madevery light in comparison with known types of speech coil formers.

In the arrangement of Figure IV the portion 6 of the speech coilcomprises longitudinal elements of different stiffnesses as before, butin this case the variations in stiffness are produced by corrugations inthe different sectors: for example the sector H has only fourcorrugations; the element 12 has eight corrugations; the element l3 hastwelve corrugations and the element I4 has sixteen corrugations; thesecorrugations all being of the same length, and height as shown inFigures IV and V. Alternatively the difference in stiffness may beproduced by making the corrugations lie at an inclination to thedirection of the axis of the coil or by making them of different heightor length or thickness. It will be noted that the superficial area ofeach longitudinal element is different, the area of an element with alarge number of corrugations being greater than that of an element witha small number of corrugations.

Figure VI shows a horn with a progressive variation of stiffness whichis produced by a progressive variation in thickness of the wall of thehorn around its'circumference. This variation is shown as being uniformin the drawings but may take place in a series of steps as in the caseof the speechcoil. An end view of the horn of Figure VI is shown inFigure VII and it will be noted that the stiffness of quadrant l5 exwillbe non-resonant.

ceeds the stillness of quadrant ii, the stiifness oi quadrant l1 exceedsthe stiffness of quadrant I5 and the stifl'ness of quadrant l8 exceedsthat of ll. Figure VIII shows a similar construction in which thesurface of separation between the thinnest and thickest parts of thewall of the horn occurs inside the horn instead of outside.Alternatively, the horn may have a prismatic form so that itscross-section forms a polygon the sides of which vary in thickness andform a continuously progressive series.

Figure IX shows a born with a wall I9 01' uniform thickness, thevariations in stiflness in this case being produced by stiffening ribs20 placed externally, the separation of the ribs being progressivelyincreased around the circumference of the horn as shown in Figure X.Alternatively the stiii'ening ribs 20 can be placed inside. the horn, orthe variation in stiflness maybe produced by means of corrugations inthe manner described with reference to the speech coil of Figure IV.

Element ll] of Figure 11 and element l8 of Figure VII are both of verythin construction and for this reason will assist in the reproduction ofa band of very high frequencies. Similarly element 9 of Figure II andelement ii of Figure VII will assist in reproduction of a band of tonesof lower frequency than element 10 of Figure II and element It of FigureVII, and so on. Each of the four portions as marked off in the drawingswill be resonant to a band of different frequencies and provided suchfour bands of frequencies are separated and do not overlap one anotherthe device The elimination of resonance from sound channel devices isthe principal object of this invention and devices constructed accordingto the invention show great advantage over other methods in use today.

Figure XI shows an alternative form of speech coil former thecross-section 01' which is an irregular polygon. The sides M, 22, 23,24, 25, and 26 progressively increase in width and thus form elementswhich progressively increase in stiffness.

Figure XII shows an alternative form of speech coil former thecross-section of which is a regular polygon. The sides 3i, 32, 33, 34,35 and 36 progressively increase in thickness as shown and thus formelements which progressively increase in stiffness.

The construction of Figures XI and XII and also a construction ofcircular cross-section similar to Figure I may also be used as soundchannels for conducting sound.

Figures XIII and XIV show loud-speaker horns in which the progressivevariation in stillness is obtained in the same way as in Figures XI andXII respectively.

Figure XV shows a rear view of a construction of sound channel which issimilar to that of Figure XII but used to form the sides of a cabinetfor housing a loud-speaker 40. A progressive variation in the stiffnessof the walls of the cabinet is obtained by the use of stifieners 4| 42,43 and 44 of different thickness; these may be made of wood or moresuitably of sound absorbing material.

Figure XVI shows a somewhat similar construction of cabinet for aloud-speaker 40 to Figure XV but in this case the variation in thethickness (and consequently the stifl'ness) of the walls is obtained bybuilding up the walls of varying layers 01' wood or sound absorbingmaterial. The use of ribs, however, progressively spaced, appearsadvantageous in the construction of wireless cabinets. The principle ofthis invention also applies in regard to the elimination of resonanceand echo from auditoriums and music halls. Many other modifications maybe resorted to. without departing from the spirit of the invention, andI desire therefore to claim the invention broadly, limited only by thescope of the appended claims.

I claim:

1. An acoustical device comprising a sound channel the wall of whichprogressively varies in thickness around its cross-sectional periphery,thereby providing a progressive variation in stifl ness around thecross-sectional periphery of the device.

2. An acoustical device comprising a sound channel the walls of whichprogressively increase in stiffness around the periphery of eachcrosssection taken along its axis, from a point of minimum stifi'ness toa point of maximum stiiiness.

3. An acoustical device comprising a tapering sound channel of similarcross-section at each point along its axis, the wall of said soundchannel increasing progressively in stiffness around the periphery ofeach cross-section from a point of minimum stiffness to a point ofmaximum stillness.

4. An acoustical device for guiding the passage of sound waves through avolume .of air comprising a tapering sound channel of circularcrosssection at each point along its axis, the wall of said soundchannel increasing progressively in thickness around the periphery ofeach crosssection from a. point of minimum thickness to a point ofmaximum thickness.

5. An electro-acoustical device comprising a cylindrical tube having acoil of wire wound thereon, the wall of said tube increasingprogressively in thickness around the periphery of each crosssectionfrom a point of minimum thickness to a point of maximum thickness butremaining constant in thickness along any axial section of said wall.

6. An acoustical device provided with a peripheral wall embracing avolume of air and forming an inlet opening and an outlet opening atopposite ends of the axis of said device, said peripheral wallprogressively increasing in stiffness around the periphery of across-section taken along its axis, from a point of minimum stiffness toa point of maximum stiffness.

'7. An electro-acoustical device comprising a cylindrical tube having acoil of wire wound thereon, the wall of said tube being provided withlongitudinal corrugations which are so chosen that said wallprogressively increases in stiffness around the periphery of across-section taken along its axis, from a point of minimum sti finessto a point of maximum stifi'ness.

8. An electro-acoustical device comprising a cylindrical tube having acoil of wire wound thereon, the wall of said tube comprising a pluralityof layers of different widths but of the same axial length so as tocause a progressive variation in thickness around the periphery of across-section taken along its axis, from a point of minimum thickness toa point of maximum thickness.

ATHOL ERNEST NEVILLE LAWRANCE.

